Springboot自動裝配之註入DispatcherServlet的實現方法

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原理概述

Springboot向外界提供web服務，底層依賴瞭springframework中的web模塊（包含但不限於spring mvc核心類DispatcherServlet）來實現

那麼springboot在什麼時機向容器註入DispatcherServlet這個核心類的呢
註入的流程還是遵循瞭自動裝配流程，在springboot框架裡默認提供瞭該自動裝配的支持

在jar包裡的spring.factories文件裡有個 org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration配置

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration(proxyBeanMethods = false)
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass(DispatcherServlet.class)
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)
public class DispatcherServletAutoConfiguration {
	/*
	 * The bean name for a DispatcherServlet that will be mapped to the root URL "/"
	 */
	public static final String DEFAULT_DISPATCHER_SERVLET_BEAN_NAME = "dispatcherServlet";
	/*
	 * The bean name for a ServletRegistrationBean for the DispatcherServlet "/"
	 *
	public static final String DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME = "dispatcherServletRegistration";
	// ... 省略代碼
	}

在DispatcherServletAutoConfiguration中有兩個內部類（配置類） DispatcherServletConfiguration、DispatcherServletRegistrationConfiguration和兩個對應的Condition類DefaultDispatcherServletCondition、DispatcherServletRegistrationCondition

DispatcherServletConfiguration

DispatcherServletConfiguration是DispatcherServletAutoConfiguration 的一個內部類，並被 @Configuration標註，會被容器自動掃描到；其有兩個方法： 1、dispatcherServlet；2、multipartResolver

	@Configuration(proxyBeanMethods = false)
	@Conditional(DefaultDispatcherServletCondition.class)
	@ConditionalOnClass(ServletRegistration.class)
	@EnableConfigurationProperties({ HttpProperties.class, WebMvcProperties.class })
	protected static class DispatcherServletConfiguration {

// @A
		@Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
		public DispatcherServlet dispatcherServlet(HttpProperties httpProperties, WebMvcProperties webMvcProperties) {
			DispatcherServlet dispatcherServlet = new DispatcherServlet();
			dispatcherServlet.setDispatchOptionsRequest(webMvcProperties.isDispatchOptionsRequest());
			dispatcherServlet.setDispatchTraceRequest(webMvcProperties.isDispatchTraceRequest());
			dispatcherServlet.setThrowExceptionIfNoHandlerFound(webMvcProperties.isThrowExceptionIfNoHandlerFound());
			dispatcherServlet.setPublishEvents(webMvcProperties.isPublishRequestHandledEvents());
			dispatcherServlet.setEnableLoggingRequestDetails(httpProperties.isLogRequestDetails());
			return dispatcherServlet;
		}

// @B
		@Bean
		@ConditionalOnBean(MultipartResolver.class)
		@ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
		public MultipartResolver multipartResolver(MultipartResolver resolver) {
			// Detect if the user has created a MultipartResolver but named it incorrectly
			return resolver;
		}
	}

@A：

  • @Configuration(proxyBeanMethods = false)：配置類采用Lite模式
  • @Conditional(DefaultDispatcherServletCondition.class)：根據DefaultDispatcherServletCondition類返回值計算是否要註入，主要邏輯是檢驗Spring容器中是否已經存在一個名字為"dispatcherServlet"的DispatcherServlet
  • @ConditionalOnClass(ServletRegistration.class)：容器中必須要有ServletRegistration類
  • @EnableConfigurationProperties({ HttpProperties.class, WebMvcProperties.class })：加載HttpProperties和WebMvcProperties

@B：註入 MultipartResolver 解析類

DispatcherServletRegistrationConfiguration

該類註入的邏輯與DispatcherServletConfiguration 相同，隻不過在類上註解瞭 @Import(DispatcherServletConfiguration.class)那麼這兩個類定義就有瞭先後順序

@Configuration(proxyBeanMethods = false)
	@Conditional(DispatcherServletRegistrationCondition.class)
	@ConditionalOnClass(ServletRegistration.class)
	@EnableConfigurationProperties(WebMvcProperties.class)
	@Import(DispatcherServletConfiguration.class) //@A
	protected static class DispatcherServletRegistrationConfiguration {

		@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
		@ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
		public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet,
				WebMvcProperties webMvcProperties, ObjectProvider<MultipartConfigElement> multipartConfig) {
			DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,
					webMvcProperties.getServlet().getPath());
			// 設置名稱		
			registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
			registration.setLoadOnStartup(webMvcProperties.getServlet().getLoadOnStartup());
			multipartConfig.ifAvailable(registration::setMultipartConfig);
			return registration;
		}
	}

其中，DispatcherServletRegistrationBean繼承自ServletRegistrationBean，主要為DispatcherServlet提供服務。DispatcherServletRegistrationBean和DispatcherServlet都提供瞭註冊Servlet並公開DispatcherServletPath信息的功能

面試點

spring mvc和spring boot的關系，相信讀瞭上面的文章會說出一兩點；

到此這篇關於Springboot自動裝配之註入DispatcherServlet的文章就介紹到這瞭,更多相關Springboot註入DispatcherServlet內容請搜索WalkonNet以前的文章或繼續瀏覽下面的相關文章希望大傢以後多多支持WalkonNet！

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